Positive electrode active material, positive electrode, and nonaqueous-electrolyte secondary battery

Abstract

Provided is a positive electrode active material giving nonaqueous-electrolyte secondary batteries superior in cycle characteristics. The positive electrode active material according to the present invention includes a lithium-containing composite metal oxide having the composition represented by the following General Formula (1):LiFeMPSiO  (1)(wherein M is at least one metal element selected from Zr, Sn, Y, and Al, 0.05<x<1, and 0.05<y<1), characterized in that: the positive electrode active material is in the single crystalline phase of the lithium-containing composite oxide represented by General Formula (1) when 1>z>0.9 to 0.75 or 0.25 to 0.1>z>0;the positive electrode active material has two crystalline phases of the lithium-containing composite oxides represented by the following General Formulae (2) and (3) when 0.9 to 0.75>z>0.25 to 0.1:LiFeMPSiO  (2)(wherein 0.75 to 0.9≦a≦1.00, 0.05<x<1, and 0.05<y<1); andLiFeMPSiO  (3)(wherein, 0≦b≦0.1 to 0.25+x, 0.05<x<1, and 0.05<y<1), andwhen the product of the lengths of the b and c axes of the unit cell of the lithium-containing composite oxide of General Formula (2) is designated as bc1 and the product of the lengths of the b and c axes of the unit cell of the lithium-containing composite oxide of General Formula (3) as bc2, α, which is defined by equation α=(bc2)/(bc1), is 0.99<α<1.01.